It is known in the art to manufacture electrical circuits in a modular implementation such that each modular electric circuit includes a plurality of electrical elements interconnected in a predetermined order to form the electrical circuit. Several approaches have been used to manufacture modular electrical circuits which include formation of the circuits in a planar configuration or as multi-layer modules.
In a planar configuration, best shown in FIG. 1, passive electrical elements are created on a single substrate 10 in a sequential manufacturing process. These electrical elements are then further connected each to the other by conductors 12. For example, in order to fabricate a filter (either a bandpass filter, low pass filter, or high pass filter) in a planar configuration, the resistors 14, inductors 16, and capacitor(s) 18 are formed at predetermined locations on the substrate 10 in sequential operational steps. Further, conductors 12 and contact pads 20 are deposited on the surface of the substrate 10 to couple the passive elements into a single circuit 22. To create the conductors 12, contact pads 20, resistors 14, inductors 16, and capacitor(s) 18, different manufacturing processes may be implemented which are known to those skilled in the art. Such processes may include thin film or thick film techniques, as well as hybrid or integration manufacturing techniques. The modular electrical circuits in planar configuration are relatively simple structures in which no via holes are needed to cross through the substrate 10 and which are easily repairable. However, this approach has several shortcomings. Initially, the circuit implemented as a planar formation uses a large area of the substrate 10. Further, during sequential operational processes, the components (electrical elements) created in the previous operational steps, are exposed to multiple “firing” cycles, that may decrease the yield or quality of electrical circuits.
Another approach to manufacturing modular electrical circuits, i.e., multi-layer modules, as shown in FIG. 2, employs depositing of a polyimide layer 24 (preferably by spin-coating of polyimide) on the surface of a supporting substrate 26 (made from silicon, GaAs, AlN, etc.), and building up basic components such as resistors, inductors, capacitors, and conductors by sequential layering. This technique may be accomplished by using thin film fabrication processes. Specifically, after spin-coating the polyimide layer 24 on the surface of the substrate 26, a first layer 28 is deposited through sputtering or by chemical vapor deposition on the surface of the polyimide layer 24. Subsequently sequential photolithography processes are performed in a predetermined order which include depositions of a photoresist on the surface of the layer 28 and exposure of the photoresist through a mask to create a desired pattern on the layer 28. This will be further followed by etching to create vias 30 extending through the layer 28; or followed by formation of passive elements of a predetermined type and topography at the areas of the layer 28 uncovered during photolithography. The conductors and contact pads may also be deposited onto the surface of the layer 28 to interconnect the elements 32 in predetermined fashion in layer 28 which allows coupling to the passive elements of another layer 34 through the vias 30.
When the pattern of passive elements and/or metal conductors is formed on the first layer 28, another thin film, i.e., the second layer 34, is deposited by sputtering or by chemical vapor deposition on the surface of the first layer 28. Subsequently sequential photolithography steps are performed to form desired passive elements and/or metal conductors on the second layer 34. The layer-by-layer sequential process is continued until all constituents needed for an electrical circuit are formed and interconnected in a predetermined order within each layer as well as between layers.
The manufacture of multi-layer modules shown in FIG. 2, allows the user to create detailed features in a very accurate process. However, disadvantageously, this process is a sequential process, in which lower layers are exposed to multiple “firing” cycles, and associated therewith are unwanted multiple heat stresses. Therefore, the overall performance of such a multi-layer module depends on the earlier formed layers, which sometimes are vulnerable to heat stress common to the sequential manufacturing processes. Additionally, this approach has the shortcoming of a slow turn-around which is time and labor consuming lending to a greater fabrication expense. In addition, multi-layer modules thus created are non-trimmable structures that prevents them from being tuned to achieve the target values.
It is therefore desirable in the field of the manufacture of modular electrical circuits to find a new approach which allows the user to avoid exposure of elements of the circuits to multiple “firing” cycles, while simultaneously providing for flexibility of the process, short turn-around time and high yield of production of quality devices.